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This paper presents the results of a study of peaty sediments underlying
Trail Ridge, a prominent physiographic feature in northeast Florida. Examin-
ation of the peat provided important clues to Florida's past climate and flora.

Respectfully yours,

Steve R. Windham, Chief
Bureau of Geology

Printed for the
Florida Department of Natural Resources
Division of Resource Management
Bureau of Geology

A bed of lignitic peat underlies an extensive area of Trail Ridge, in Bradford
and Clay counties, Florida. Trail Ridge is composed largely of heavy-mineral-
bearing quartz sand which was deposited as a beach ridge by a transgressing sea.
Fossil molluscs found within the sand suggest that the beach ridge is of Late
Pliocene or Early Pleistocene age. Palynological analysis of the lignitic peat
shows that small trees, shrubs, and aquatic herbs grew in a freshwater swamp
which stood adjacent to the accumulating sand ridge. Myrica, Ilex, Magnolia,
Gordonia, and Cyrilla are among the genera which indicate that the climate in
northern Florida was subtropical at the time of peat deposition. The palyno-
flora has a modern aspect, and supports the contention that Trail Ridge is of
post-Miocene age.

ACKNOWLEDGEMENTS

This author is indebted to E. I. du Pont de Nemours and Company and the
Florida Bureau of Geology for generously supplying the samples from Trail
Ridge. Mr. Tom Garnar, Jr., of du Pont, and Charles W. Hendry, Jr., of the
Florida Bureau of Geology, deserve special thanks. Drs. Fred Pirkle and Jesse
Yeakel provided information and samples which were critical to this project,
and reviewed the manuscript. They are gratefully acknowledged.
Funding for this work was provided in part by the Coal Research Section of
the Pennsylvania State University and the South Dakota School of Mines and
Technology.

PALYNOLOGY AND PALEOECOLOGY OF A
LIGNITIC PEAT FROM TRAIL RIDGE, FLORIDA

by
Frederick J. Rich

INTRODUCTION

An extensive bed of lignitic peat lies beneath the sands of Trail Ridge, in
Bradford and Clay counties, Florida (figure 1). The organic sediment is
commonly very woody and is associated with tree trunks, stumps, and limbs.
It is usually encountered during sand dredging at the E. I. du Pont de Nemours
and Company Trail Ridge Mine, where the organic layer underlies heavy-mineral
bearing sands.
Early in 1979, the Florida Bureau of Geology, in cooperation with du Pont
was able to take two cores of dark brown, lignitic sediment from Sections 30
and 31, T 7 S, R 23 E of the Starke, Florida, quadrangle (figure 2). This paper
is a report on the palynological composition of the sediment, and presents a
discussion of the relationship between the organic sediments and the origin and
age of Trail Ridge.

LOCATION AND CHARACTERISTICS OF TRAIL RIDGE

Trail Ridge is a linear sand body which lies on the Atlantic Coastal Plain of
Georgia and northern Florida. It extends from a position near the Altamaha
River in Georgia to a point 209 kilometers south in Bradford and-Clay counties,
Florida (figure 1). According to Pirkle (1984) the ridge ranges from about 43nm
(meters) to a little more than 52 m above sea level in Georgia, and lies between
51 m and about 76 m above sea level in Florida. The ridge is composed
primarily of loose to slightly indurated quartz sand which, in some places, may
have three percent heavy minerals. Important ore minerals include ilmenite,
leucoxene, rutile, and zircon. In addition, tourmaline, kyanite, staurolite"and
other minerals are present (Pirkle, et al., 1977).
The-origin-of Trail Ridge has been a matter of debate for many years.
Doering (1960) and Alt (1974), for example, envision the ridge as having been a
spit which built southward from Georgia into Florida during some ancient
period of marine transgression. White (1970) and Pirkle (1972), on the other
hand, consider the ridge to have formed as a beach ridge along the shore line of
the coastal plain at the height of a marine transgression. The favored theory
seems to be the beach ridge hypothesis advanced by Pirkle and Yoho (1970) and
refined by Pirkle (1972), Pirkle (1977) and Pirkle, et al. (1977). According to

The author is presently at the Department of Geology and Geological Engineer-
ing, South Dakota School of Mines and Technology, Rapid City, SD 57701.

Figure 1. Position of Trail Ridge with respect to Clay, Bradford, and Putnam
counties, Florida.

Pirkle (1984), "... those hypotheses explaining Trail Ridge as a beach ridge
deposited in a wind-wave environment are more consistent with the features of
Trail Ridge sediments than are those hypotheses that explain Trail Ridge as a
spit developed in an environment dominated by current action."
While the origin of the sand which comprises the ridge may be debatable, it
seems most likely that the sand was reworked from high terraces of the Northern
Highlands, which lies west of Trail Ridge. Reworking occurred as transgressing
seas eroded into the ancient terrace deposits (Pirkle, et al., 1977).

NATURE AND ORIGIN OF THE TRAIL RIDGE PEAT DEPOSIT

The organic sediment beneath Trail Ridge has been described as a peat
(Pirkle and Yoho, 1970), though its petrographic appearance and chemical
composition are more suggestive of brown coal or lignite. Rich, et al., (1978)
note that the state of alteration of the sediment is "... similar to some lignites
from the Gulf Coast Region ... ", and that because of the unusual nature of the
peat, ... it is viewed as representing an important intermediate stage in the
alteration of organic materials from peat to brown coal or lignite."
The sediments examined in this study ranged from brownish-black, dense,
indurated material to unconsolidated peaty sand. Some core intervals consisted
of solid plugs of wood (J. Yeakel, personal communication).
If one examines the elevation of the upper surface of the woody layer, as
located by coring in the vicinity of Starke, Florida, it may be seen that the
sediment forms a fairly continuous bed beneath that part of the ridge. Un-
published data acquired by E. 1. du Pont de Nemours and Company show that
though the peat surface is irregular, it is remarkably level. Where the peat does
not exist elsewhere on the ridge, the stratigraphic interval within which it would
be expected to occur (15 to 18 m depth) is occupied by drab to olive-green clays
which appear to represent a weathered horizon (Pirkle, et al., 1977). Both peat
and weathered clay seem to have developed at the same time and occupied the
land surface atop older, sandy sediments associated with the Northern
Highlands.
Preliminary palynological investigation by Rich, et al. (1978) and Rich
( 982) show that the peat deposit near Starke was produced by freshwater trees,
shrubs, and a variety of herbaceous species. Upright trunks found at the top of
the peat layer indicate that the swamp was buried in place as marine trans-
gression occurred, and the sands of Trail Ridge began to accumulate (Pirkle,
et al., 1977).

SAMPLE PREPARATION AND ANALYSIS

Samples were taken from two core holes, designated TR 1 and TR 2. The
cores were taken about 1.5 km apart (figure 2) and, because the organic sediment

came from approximately the same depth in both holes (15 19 m below land
surface), it is assumed that the same layer of lignitic peat was cored at both
locations.
Twenty samples were crushed, then boiled for 10 minutes in a 10 percent
solution of potassium hydroxide. After thorough washing, residues were mixed
with glycerine jelly, and slides prepared. At least 200 pollen grains and spores
were counted for each sample. It was not assumed that any particular pollen/
spore type would be overrepresented, though this is often the case in modern
environments. Every grain of each identifiable taxon was included in the total
pollen/spore count.
Figures 3 and 4 display the results of the palynological analyses of core holes
TR 1 and TR 2, respectively. Each family or genus on the graphs was present in
at least one sample in an amount greater than one percent. In cases where taxa
never occurred in amounts greater than one percent [e.g., Alnus (alder), Carya
(hickory), and Liquidambar (sweet gum)], those forms were not graphed. Taxa
which have been graphed, but which periodically were not actually counted due
to their infrequency are indicated on the graphs by a T (trace).

PALYNOLOGICAL COMPOSITION OF THE SAMPLES

The palynological composition of samples from cores TR 1 and TR 2 shows
that the vegetation of the Trail Ridge swamp was generally composed of shrubs,
small trees, and herbs. Among the shrubs and small trees, Ilex (holly), Myrica
(wax myrtle), Cyrilla (ti ti), Corylus (hazel), and Gordonia (loblolly bay) were
significant. Important Herbaceous taxa included the Cyperaceae (sedges), the
fern Osmunda, and the moss Sphagnum.
In all cases, the palynoflora is composed of genera and families which are
still common in the southeastern United States.
Several other conclusions can be drawn from the graphs. If one considers
the data for TR 1 first, the following interpretations are apparent:

1) Taxa which are commonly abundant in great amounts (e.g., 20 percent or
more) in modern southeastern swamp peats are not especially abundant at any
level [note especially Quercus (oak) and Pinus (pine)].
2) Pollen of sub-tropical genera are present, notably Cyrilla, Gordonia, and
Magnolia (Plate 1).
3) Pollen of shrub genera are very common, especially Myrica (28 47 percent)
and Ilex (22 percent) (Plate 1).
4) Some of the principal genera, including Cyrilla, Gordonia, and Taxodium
(cypress) display distinct trends in their relative abundances. The first two
forms decrease in abundance with depth, while Taxodium increases.

came from approximately the same depth in both holes (15 19 m below land
surface), it is assumed that the same layer of lignitic peat was cored at both
locations.
Twenty samples were crushed, then boiled for 10 minutes in a 10 percent
solution of potassium hydroxide. After thorough washing, residues were mixed
with glycerine jelly, and slides prepared. At least 200 pollen grains and spores
were counted for each sample. It was not assumed that any particular pollen/
spore type would be overrepresented, though this is often the case in modern
environments. Every grain of each identifiable taxon was included in the total
pollen/spore count.
Figures 3 and 4 display the results of the palynological analyses of core holes
TR 1 and TR 2, respectively. Each family or genus on the graphs was present in
at least one sample in an amount greater than one percent. In cases where taxa
never occurred in amounts greater than one percent [e.g., Alnus (alder), Carya
(hickory), and Liquidambar (sweet gum)], those forms were not graphed. Taxa
which have been graphed, but which periodically were not actually counted due
to their infrequency are indicated on the graphs by a T (trace).

PALYNOLOGICAL COMPOSITION OF THE SAMPLES

The palynological composition of samples from cores TR 1 and TR 2 shows
that the vegetation of the Trail Ridge swamp was generally composed of shrubs,
small trees, and herbs. Among the shrubs and small trees, Ilex (holly), Myrica
(wax myrtle), Cyrilla (ti ti), Corylus (hazel), and Gordonia (loblolly bay) were
significant. Important Herbaceous taxa included the Cyperaceae (sedges), the
fern Osmunda, and the moss Sphagnum.
In all cases, the palynoflora is composed of genera and families which are
still common in the southeastern United States.
Several other conclusions can be drawn from the graphs. If one considers
the data for TR 1 first, the following interpretations are apparent:

1) Taxa which are commonly abundant in great amounts (e.g., 20 percent or
more) in modern southeastern swamp peats are not especially abundant at any
level [note especially Quercus (oak) and Pinus (pine)].
2) Pollen of sub-tropical genera are present, notably Cyrilla, Gordonia, and
Magnolia (Plate 1).
3) Pollen of shrub genera are very common, especially Myrica (28 47 percent)
and Ilex (22 percent) (Plate 1).
4) Some of the principal genera, including Cyrilla, Gordonia, and Taxodium
(cypress) display distinct trends in their relative abundances. The first two
forms decrease in abundance with depth, while Taxodium increases.

Graphs for core hole TR 2 also lead to several conclusions, as follows:

7) Common over-producers of modern pollen in southeastern swamps are, again,
not overly abundant. Note the Quercus is generally uncommon, Taxodium is
never more than 10 percent of total pollen/spores, and Pinus is always less than
20 percent.
2) Pollen of sub-tropical genera are present, including Cyrilla, Magnolia, and
Gordonia.
3) Shrub pollen comprises the highest percentage of palynomorphs at most
levels, including cf. Corylus, llex,Cyrilla, and Myrica.
4) The fern Osmnunda is quite abundant near the bottom of the core, and
Sphagnum is common in many samples.
5) There are distinct stratigraphic changes in the relative abundances of certain
taxa. Cyrilla, for example, gradually rises in abundance in the upper half of core
TR 2, while Osmunda is most abundant at the base and diminishes rapidly as one
proceeds upward in the core.

PALEOECOLOGICAL INTERPRETATIONS

The fact that Trail Ridge is believed to be a marine shoreline deposit poses
the possibility that the peat-producing swamp buried beneath the ridge could
have been of either freshwater or brackish water origin. Some of the common
genera from the Trail Ridge samples are, unfortunately, paleoenvironmentally
undiagnostic in this regard. Certain modern species of flex and Myrica, for
example, are common inland (i. cassine and M. cerifera) while others are
common very near shore (/. vomitoria and M. gale). These genera could, thus,
be expected to occur in both freshwater and brackish water sediments.
However, many of the other fossil genera strongly indicate that the peat-forming
plants grew in freshwater. Nyssa, Magnolia, Taxodium, Cyrilla, and Sphagnum
are among the freshwater indicators. Furthermore, Nyssa, Magnolia, Gordonia,
and Cyrilla have been shown to exhibit very restricted pollen dispersal potential
(Rich and Spackman, 1977; 1979). The presence of their pollen in the TR 1 and
TR 2 samples is interpreted to mean that the plants actually grew at the sites of
deposition.
Taxodium is present in unexpectedly small amounts in the Trail Ridge
samples. This is especially true of the TR 2 samples, where relative abundance
varies from 0.40 9.6 percent. Rich (1979) encountered Taxodium in amounts
of 25 50 percent in a wide variety of Okefenokee Swamp peats. Cohen (1975)
found that Taxodium values ranged between 4.8 55.6 percent for peats from
seven modern Okefenokee environments. Taxodium percentages in the TR
samples are usually less than 10 percent. This indicates that the trees were not
dominant, or even common during much of the time of peat deposition.

Quercus and Pinus are similarly uncommon in the TR cores. Within TR 1
samples, Quercus pollen ranges from 0.0 4.5 percent of total pollen and spores,
and in TR 2 samples the range is 0.41 2.7 percent. Cohen (1975) determined a
range of average values of 4.2 10.3 percent for Quercus in seven Okefenokee
environments and found that the polten never occurred as less than 3.0 percent
of total pollen/spores. Pinus appears in TR 1 samples in amounts between 2.2 -
8.4 percent, while in TR 2 samples the range is 3.1 16.0 percent. Cohen (1975)
identified at least 6.0 percent Pinus in all his modern Okefenokee environments,
and identified average values of 12.4 36.0 percent.
The low levels of Quercus and Pinus pollen in the TR samples indicate that
the trees did not grow near the sites of peat deposition. This is somewhat para-
doxical because the nearby sandy beach ridge should have been a very suitable
place for the trees to live. It is possible that the trees lived just far enough from
the swamp that their pollen failed to accumulate in large quantities and were
masked by the local, heavy production of shrub pollen.
Aside from the gross compositional characteristics of the TR samples, there
are detailed vertical changes in palynomorph composition which reflect the plant
community successions at the sample sites. In the lower half of TR 1, an abun-
dance of Taxodium, Ilex, Myrica, and cf. Corylus, accompanied by
Myriophyllum (water-milfoil) and Graminae pollen suggests that cypress forest,
with shrubby undergrowth and clear, standing water occupied the site. At
16.33 m below the surface, Taxodium pollen declines noticeably, while pollen
and spores of herbaceous species become more abundant (Cyperaceae, Osmunda,
and eventually, Sphagnum and Woodwardia). Between 16.33 15.74 m
Gordonia and Cyrilla both occupied the site, accompanied by Ilex, Myrica and
cf. Corylus. The change from a bald cypress-dominated community to one
inhabited by shrubs and herbs could have been due to environmental changes
brought about by a period of drought and forest fires. J. Yeakel (personal
communication) reports that a layer of charcoal was found in core TR 1 at
16.5 m, just below the level of palynofloral transition.
Plant succession at the TR 2 site was similar in some respects to that at
TR 1, though there were differences in detail. For example, between 17.83 -
18.66 m an herbaceous assemblage with abundant ferns and scattered shrubs
dominated. This is shown by an abundance of Osmunda spores, with
Cyperaceae, Sagittaria (arrowhead, or duck potatoe, and Graminae pollen,
Woodwardia spores and Myrica, Ilex, and cf. Corylus pollen. Virtually all taxa,
including Taxodium, decrease in abundance markedly at 17.83 m. Myrica and
Cyrilla show obvious increases at that depth. This stratigraphic level is the same
as that within the TR 1 core where Taxodium concentrations dropped. The
fire and dry conditions which altered vegetation at the TR 1 site evidently had a
similar affect on plants at TR 2. Following the disturbance, a shrub-dominated
swamp developed and produced the sediment between 17.83 16.76 m. Note
that, at both locations, Cyrilla rose to prominence toward the end of peat
deposition.

AGE OF THE TRAIL RIDGE LIGNITE PEAT

The lignitic peat must be somewhat older than Trail Ridge, and if the age of
the ridge were well-established, the peat could be dated. Unfortunately, the age
of Trail Ridge is as debatable as its origin. Alt (1974) has proposed a Miocene
age for the ridge, while Pirkle and Yoho (1970) contend that the sandy body is
no older than Pliocene. Other authors (Cooke, 1939; Hoyt and Hails, 1969)
maintain that the ridge, also known as the Wicomico shoreline, is of Early
Pleistocene age.
Pirkle and Czel (1983) have identified mollusc fossils taken from a series of
drill holes which penetrated Trail Ridge in southern Georgia. The molluscs all
represent extant, shallow marine species. The lack of extinct species adds weight
to the idea that the fossils and, hence, the ridge can be no older than Late
Pliocene age.
Rich (1982) stated that the Trail Ridge peat is of Early Pleistocene age,
though his conclusion was based upon the work of Pirkle and Yoho (1970) and
other authors previously cited here. Further palynological investigation of the
TR samples has not gone much further toward establishing the age of the Trail
Ridge peat, though some useful observations can be made which relate Trail
Ridge samples to other deposits from the southeastern United States.
Elsik (1969) has been able to construct a generalized pollen profile for Gulf
Coast sediments of Miocene through Pleistocene age. Within the Miocene,
Quercus is abundant, constituting as much as 20 percent of the pollen assem-
blage. The Miocene-Pliocene transition is difficult to delineate though Elsik
states that Ambrosia and Helianthus-type composites are most common in the
Pliocene, even more common than oak. There is a decrease in Compositae
(sunflowers, daisies, etc.) and Quercus pollen as Pleistocene deposits are
encountered, and a general increase in the relative abundance of Pityosporites,
A/nus, and Taxodium. The fungal spore, Exesisporites also increases in
abundance in Pleistocene deposits. Darrell (1975) reported on the palynological
composition of strata from the Georgia coastal plain. There, Miocene and
Pliocene deposits are characterized by Ouercus-type pollen, while gymnosperm
pollen generally are either missing or are of minor significance. The exception
is that Pinus pollen is more abundant in Pliocene deposits than it is in Miocene
sediments.
In light of Elsik's and Darrell's conclusions, the following observations can
be made regarding the Trail Ridge pollen assemblages:

1. Quercus is of very low abundance in the TR samples. This would suggest a
post-Miocene age for the peat.
2. Composite pollen are very low in abundance at all TR sample intervals. TR 1
samples average 0.50 percent, while TR 2 samples average 0.52 percent. These
would suggest a Pleistocene age for the peats.

3. Alnus is missing from all but two Trail Ridge samples, and then it appears as
less than one percent. The absence of Alnus makes the TR samples unlike
known Pleistocene deposits.
4. Taxodium pollen is present at very low levels in TR 2 especially, and Pinus is
low in TR 1 samples. These facts make the samples unlike Pleistocene deposits
from the Gulf Coast.

The palynological composition of the Trail Ridge samples is equivocal as
regards the age of the deposit. This is unfortunate because all other means of
dating the ridge are equally ambiguous. Perhaps the one safe conclusion that can
be drawn is that, because no extinct species were identified in the TR samples,
and because oak pollen is not abundant in them, the peat and, therefore, the
ridge are not of Miocene age.

SUMMARY

Samples of dark brown lignitic peat were taken from beneath Trail Ridge, in
northern Florida. Palynological analysis of the samples shows that a sub-tropical
swamp composed mostly of small trees, shrubs, and aquatic herbs existed in the
area prior to deposition of the ridge. The swamp developed near sea level on the
reworked terrace sands of the Northern Highlands during Pliocene or Early
Pleistocene time. As sea level rose, beach-ridge sands migrated laterally over the
swamp and eventually killed and buried the plants and the peat they produced.
The actual age of the swamp, and the age of Trail Ridge are difficult to
determine except that neither appears to be of Miocene age.

PLATE 1

Pollen of trees and shrubs
identified in Trail Ridge core samples.

All figures 900x.

1. Myrica sp.

2. Ilex sp.

3. Magnolia sp.

4. Gordonia cf. lasianthus

5. Cyrilla cf. racemiflora

PLATE 1

2

4i

3. Alnus is missing from all but two Trail Ridge samples, and then it appears as
less than one percent. The absence of Alnus makes the TR samples unlike
known Pleistocene deposits.
4. Taxodium pollen is present at very low levels in TR 2 especially, and Pinus is
low in TR 1 samples. These facts make the samples unlike Pleistocene deposits
from the Gulf Coast.

The palynological composition of the Trail Ridge samples is equivocal as
regards the age of the deposit. This is unfortunate because all other means of
dating the ridge are equally ambiguous. Perhaps the one safe conclusion that can
be drawn is that, because no extinct species were identified in the TR samples,
and because oak pollen is not abundant in them, the peat and, therefore, the
ridge are not of Miocene age.

SUMMARY

Samples of dark brown lignitic peat were taken from beneath Trail Ridge, in
northern Florida. Palynological analysis of the samples shows that a sub-tropical
swamp composed mostly of small trees, shrubs, and aquatic herbs existed in the
area prior to deposition of the ridge. The swamp developed near sea level on the
reworked terrace sands of the Northern Highlands during Pliocene or Early
Pleistocene time. As sea level rose, beach-ridge sands migrated laterally over the
swamp and eventually killed and buried the plants and the peat they produced.
The actual age of the swamp, and the age of Trail Ridge are difficult to
determine except that neither appears to be of Miocene age.

Rich, F. J., 1979, The Origin and Development of Tree Islands in the Okefen-
okee Swamp, As Determined by Peat Petrography and Pollen Strati-
graphy: unpubl. Ph. D. thesis, The Pennsylvania State University.

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